Numerous means have been sought to improve the fuel-efficiency of moving bodies and, especially, moving bluff bodies by reducing their aerodynamic drag. In the field of surface transportation, and particularly in the long-haul trucking industry, even small improvements in fuel efficiency can reduce annual operating costs significantly. It is therefore advantageous in the design of a vehicle to reduce drag forces, thereby increasing the aerodynamic properties and efficiency of the vehicle.
The over-the-highway cargo-hauling tractor-trailer combination is one vehicle that experiences excessive aerodynamic drag. Generally described, tractor-trailer combinations typically include a tractor having a so-called fifth wheel by which a box-like semi-trailer may be attached to the tractor by an articulated connection for transportation of the cargo trailer. In addition to the gap between the tractor and trailer and the space behind the trailer rear doors, other areas around the combination generate drag as the combination traverses across the ground. Some of these areas include the undercarriage of the tractor and/or trailer, which is comprised of groupings of various drag-producing components. These drag-producing components of a tractor-trailer undercarriage customarily include axles, mud flaps, tires, and other components, such as brake components, suspension components, and longitudinal and transverse structural support members well known in the art, etc.
Most large long-haul tractor-trailer combinations similar to those described above exhibit less than optimal aerodynamic performance during highway operation. At highway speeds, these conventional combinations develop a substantial amount of turbulent airflow in and around the undercarriage thereof. This turbulence results in significant aerodynamic drag, increasing both fuel consumption and Nitrogen Oxide (NOx) emissions of the tractor.